Gas turbines coupled to generators are used to convert fossil energy into electrical energy. For this purpose, along its rotor shaft a gas turbine has a compressor, a combustion chamber and a turbine. During operation, the compressor draws in ambient air and compresses it. Then the compressor air is mixed with a fuel and fed to the combustion chamber, where the mixture is burnt to form a hot working medium which flows into the turbine, which is connected downstream of the combustion chamber and in which blades and vanes are provided. The guide vanes, which are secured to the housing of the turbine, divert the working medium onto the rotor blades secured to the rotor, so that they set the rotor in rotary motion. The rotational energy of the rotor which is taken up in this way is then converted into electrical energy by the generator coupled to the rotor.
The rotor blades of the gas turbine are exposed to mechanical stresses, in particular caused by centrifugal force. In particular under the action of the high temperatures of the working medium, cracks may form in the blade material, shortening the service life of the rotor blades. Long-term stresses can then lead to crack growth. Under the loads which are present, the blade then fails, with the blade fracturing or fragments becoming detached. This can lead to damage to the blades and vanes located downstream as seen in the direction of flow of the working medium. Crack formation and crack propagation therefore needs to be monitored at regular servicing intervals.
U.S. Pat. No. 6,490,791 has described a method in which in a service process cracks in the trailing edge of a turbine blade are eliminated by cutting back the trailing edge. The aerodynamic losses caused by the shortening of the trailing edge are kept at a low level by subsequent rounding of the blade profile.
JP 2000018001 shows a rotor blade for a gas turbine in which notches extending in the radial direction are introduced at the stripping edge. This leads to a reduction in the thermal stresses in this region.
JP 10299408 shows a gas turbine guide vane which in the transition region from platform to vane profile has elliptical relief notches, the main axis of which is oriented transversely with respect to the main stressing direction, in order to avoid crack growth.